Kiev Cameras, etc.

What the Heck is Bokeh?

There is much written on the net about this
elusive subject, and I won't attempt to provide the etymology of the
word (is it Japanese or not?) to compete with it. Suffice to say that
different lens designs have an effect on the appearance of the
out-of-focus areas in photographs.

Some photographic styles commonly use selective
focus to bring the viewer's attention to the subject. That means the
subject is focused but the non-subject areas are not. If those unfocused
areas are busy and distracting, the objective of bringing attention to
the subject is lost. That's why portrait photographers in particular
care about bokeh.

There are a couple of myths about bokeh:

Bokeh is controlled by the roundness of the
lens diaphragm.

Faster lenses have better bokeh.

Both of these are, at the very least, not the
whole story, as we will see.

An out-of-focus highlight will be represented as a
disk. If that disk is uniformly bright, the bokeh is, in my opinion,
neutral. This is common with highly corrected prime lenses. The
literature suggest that over-correction of spherical aberration causes
the disk of the out-of-focus highlight to have a bright edge. I call
this bright-edge bokeh, and it's a close cousin of another
distracting effect, known as double-line bokeh, where
out-of-focus linear details are rendered as parallel lines. These are
examples of poor bokeh.

Lens designs that provide good performance but
leave a residue of uniformly under-corrected spherical aberration
produce a disk with a faded edge, that I call soft-edge bokeh.

Some lens designs are associated with good bokeh,
while others are associated with poor bokeh. The three lens types that
are usually found in normal and short telephoto lenses are the
traditional Tessar, a double-gauss design like the Planar, and the
traditional Sonnar. Sonnars are thought to have the best bokeh, while
Tessars are described over and over again as having "clumpy" bokeh that
is acceptable to some and not to others. Double-gauss lenses are hard to
pin down. Some double-gauss designs have reputations for terrible bokeh,
like the Shneider Xenotar, and others are famous for good bokeh, like
the Canon Serenar 50/1.8 that was used on their rangefinder camera back
in the 50's and 60's.

The Tessar design is a refinement of the old
triplet design. It minimizes chromatic aberration and provides good
sharpness, but does not perform really well at wide apertures. It used
few elements (only two or three groups), so it worked well in
uncoated lenses. The Planar/double-gauss design is quite old--over 100
years--but it required 6 elements in at least four groups. Performance
without anti-reflection coatings was poor, with lots of flare. So, this
design did not gain in popularity until lens coatings were used. The
Sonnar design was intended to provide excellent wide-aperture
performance without so many air surfaces. The first really fast normal
lenses were Sonnar designs, and even as late as the 50's most fast
normals were variations of it. But the Sonnar design had a fault when
used as a normal: The glass got too close to the film and did not allow
room for a reflex mirror. Thus, the Sonnar design could not be used for
normal lenses in single-lens reflex cameras what had a mirror box
between the lens and the film.The Sonnar design has therefore shifted to
longer focal lengths where sufficient clearance could be attained.

In the last couple of decades, lens design has
enjoyed a couple of breakthroughs. One is computer optimization, using
the modulation transfer function instead of ray-tracing. MTF provides a
measure not only of acutance and resolution, but also how they interact
with contrast to accurately represent fine detail in the photograph. The
other breakthrough is low-dispersion and high-refractive glass. These
two breakthroughs, coupled with advanced multi-coatings, have made
complex designs possible, especially in with zoom lenses.

Lenses Tested

To demonstrate and compare bokeh, I have assembled
a range of lenses all in the 120-135mm focal length. These are commonly
used as short portrait lenses in medium format and long portrait lenses
in 35mm. (They are very long for portraits using an APS-sized sensor,
but the longer working distance proves to be important in keeping
depth-of-field narrow). I chose this focal length for several reasons:
1.) it sits between the popular 80-100mm range in small cameras and the
150-180 range in medium-format cameras, and thus I could throw in some
examples from those categories without the change in focal length
ruining any hope of comparison. 2.) This focal range is considered a
working portrait range in both small and medium-format cameras, and so
lenses in this range are more likely to be designed with good bokeh in
mind. 3.) I happened to own a wide variety of lenses in this range,
including at least one example from the three major lens designs
described above.

Zeiss Jena 180/2.8 Sonnar added to the test,
here compared with the 135/3.5 Sonnar. It's heavy in addition to being
big.

Lens Description

Comments

135mm f/3.5
Carl Zeiss Jena
MC-Sonnar

M42 mount and adapted to
Canon EF. This lens is a four-element Sonnar design with
multicoating, and was intended for use in Practika and Pentacon
35mm cameras made in the former East Germany. Produced in the
1980's, but designed in 1965.

139mm f/4.5
Bausch and Lomb
Tessar

A barrel lens mounted on a
Pentacon Six bellows, which are adapted to Canon EF. This lens
is by far the oldest in the test. It's a pre-war uncoated lenses
intended for use on enlargers. Enlarger lenses would not be
expected to be optimized for bokeh, and this lens does nothing
to refute that assertion. I use it for copy work in medium
format. Produced in the 1930's.

120mm f/2.8
Carl Zeiss Jena
MC-Biometar

This five-element
double-gauss lens is a variation on the Planar design. The
diaphragm was malfunctioning on this lens and so it was tested
only wide open. The mount is Pentacon Six medium format, adapted
to Canon EF. Produced in the 1980's from a 1950's design. Many
buy this lens to escape the often poor bokeh of the Vega (see
below), but is it really better?

75-150mm f/3.5
Nikon Series E

The Nikon EM was intended to
be a low-cost entry into the SLR market many years ago. The
Series E lenses for it were also targeted to a low price point,
which is why they are not Nikkors. I included it because when it
comes to bokeh, assumptions without testing are dangerous, and
it might turn out to be a gem. It has a Nikon AI mount, but I
have an adaptor. The lens dates probably from the early 80's,
and I expect the design was a stock design in the Nikon lens
range. It's a good lens to test whether lens complexity means
bad bokeh, especially if the lens is cheap.

120mm f/2.8
Arsenal (Kiev)
Vega MC

Arsenal is a Ukrainian
manufacturer, and also produces the Kiev line of cameras. The
lens is a double-gauss design with six elements in four groups.
It is known for being sharp, and in some circumstances for
producing unsatisfying bokeh. It's in an Pentacon Six mount. The
Vega is likely a 70's or earlier design, and the lens dates from
the 80s.

70-200mm f/4L
Canon
L-series

This is a highly regarded
L-series premium zoom lens from Canon, designed in the late
1990's. It is by far the most expensive lens in the lineup, but
also the most complex with 14 elements.

135mm f/2.8
Canon
Soft-Focus

The soft-focus effect on this
lens seems to be switchable spherical aberration. I find the
effect unsatisfying, but the lens is still quite usable with the
soft-focus switched off. It's faster than the Zeiss Jena 135 at
the top of the list, but is it better? This lens was designed in
the 80's or 90's.

85mm f/2.0
LSOZ
Jupiter-9 MC

This lens is a copy of a
Sonnar, and is made in Russia for use on Zenit cameras with an
M42 mount. It has a preset aperture with many blades and
produces a round aperture at all settings. A proper test of this
lens would compare it with the Canon 85/1.8, which is known for
good bokeh, and various 80mm medium-format double-gauss lenses.
I'll save that for a future test.

180mm f/2.8
Carl Zeiss Jena
MC-Sonnar

This medium-format portrait
telephoto is perhaps the most classic of all Sonnars, being a
direct descendent of the original Olympia Sonnar developed for
us in the 1936 Olympics. F/2.8 is quite fast at this focal
length, and with coverage for medium format, the lens is quite
large. I included this lens to compare it with the Canon
70-200/4L zoom, and to compare it with the faster (f/2.8) lenses
in the test. It is famous in medium-format circles for having
outstanding bokeh, and even non-photographers can pick images
made with this lens out of a crowd.

Test Scenarios

Test conditions include a near item that would
serve as a focus target. A far item would provide a sampling of
out-of-focus details to provide the comparison. There were three test
scenarios. The first is a wine bottle used as a focus target, with a
crystal wine glass and crystal candlestick in the background. The facets
of the crystal provides a range of out-of-focus highlights. This test
was conducted at f/4 for all the lenses (except the Tessar, at f/4.5).
This test did well for looking at out-of-focus specular highlights, but
did not reveal general rendering of out-of-focus backgrounds clearly.

The second scenario used a small Hopi Kachina doll
as the focus target. A larger doll in the background tested out-of-focus
patches of color and a range of details. A glass vase next to the doll
in the background provided some out-of-focus specular highlights. I used
a striped Mexican blanket as a background to provide out-of-focus linear
elements. This test was conducted at f/4 and at f/11. This test gave
different results, demonstrating that lenses perform differently in
different scenarios. To render the background Kachina doll more out of
focus, a third scenario was set up.

The third scenario is a slight variation of the
second, to get the items within the field of view and minimum focus
distance of the 180mm Sonnar, and to put the background doll more out of
focus. This test was conducted at f/4 only with the Sonnar and the Canon
70-200/4L zoom, and then it was repeated with a selection of the lenses
at their maximum apertures.

Scenario 3 Subject arrangement. Camera was
about four feet to the left of the frame.

Lighting for all tests was the same: A bank of
tunsten floodlights to provide plenty of specular highlights.

The camera was a Canon 10D 6-megapixel digital
camera with a 15x23mm sensor. 135mm is nearly five times the normal
focal length of 28mm for this format. White balance was set to tungsten
(2800 degrees Kelvin). Images were shot in raw mode, and batch
converted with no processing to high-quality JPEG files of 500x333
pixels. There are some JPEG artifacts in the images, but the JPEGs do
not lead me to different conclusions than the original images. The
camera was mounted on a very sturdy Bogen tripod (the largest in
Manfrotto's line and intended for large-format view cameras). Exposure
times were generally 1/8 second at f/4, 1 second at f/11, and 1/15 at
f/2.8, with an ISO setting of 200.

Test Scenario 1, Wine Glass at f/4.

135/3.5

Zeiss Jena

MC-Sonnar

Edge: Slight bright-line

Double-line: None

Aperture shape: Slight

Overall effect: Pleasing

139/4.5

Bausch and Lomb

Tessar

Edge: Pronounced bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: Distracting

120/2.8

Zeiss Jena

MC-Biometar (at f/2.8 due to faulty
aperture)

Edge: Pronounced bright-line

Double-line: Apparent

Aperture shape: Slight

Overall effect: Distracting

75-150/3.5

Nikon

Series E (at ~135)

Edge: Very slight bright-line

Double-line: None

Aperture shape: Slight

Overall effect: Pleasing

120/2.8

Arsenal

Vega MC

Edge: Slight bright-line

Double-line: Apparent

Aperture shape: Slight

Overall effect: Neutral

70-200/4L

Canon (at ~135)

Edge: Slight bright-line

Double-line: Slight

Aperture shape: None (lens is wide open)

Overall effect: Pleasing

135/2.8

Canon (no SF)

Edge: Slight bright-line

Double-line: Slight

Aperture shape: Slight

Overall effect: Neutral

85/2

Jupiter

Edge: Slight bright-line

Double-line: None

Aperture shape: None

Overall effect: Pleasing

Test Scenario 2, Kachina Dolls at f/4

135/3.5

Zeiss Jena

MC-Sonnar

Edge: Very slight bright-line

Double-line: None

Aperture shape: Very slight

Overall effect: Pleasing

139/4.5

Bausch and Lomb

Tessar

Edge: Pronounced bright-line,
with bright center dot

Double-line:
None

Aperture shape: None

Overall effect: Distracting

120/2.8

Zeiss Jena

MC-Biometar (at f/2.8 due to faulty
aperture)

Edge: Pronounced bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: Distracting

75-150/3.5

Nikon

Series E (at ~135)

Edge: Very slight bright-line

Double-line: None

Aperture shape: Slight

Overall effect: Pleasing

120/2.8

Arsenal

Vega MC

Edge: Slight bright-line

Double-line: None

Aperture shape: Slight

Overall effect: Neutral

70-200/4L

Canon (at ~135)

Edge: Slight bright-line

Double-line: Slight

Aperture shape: None (lens is wide open)

Overall effect: Pleasing

135/2.8

Canon (no SF)

Edge: Slight bright-line

Double-line: Slight

Aperture shape: Slight

Overall effect: Neutral

85/2

Jupiter

(at f/2 to provide similar apparent focus)

Edge: Pronounced bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: Distracting

Test Scenario 2, f/11

Out of focus details were too small to assess edge
effects. They could be seen at full enlargement, but were not apparent
and normal viewing distances and therefore I decided they were not
important. Instead, in this section, I'm curious whether there is much
noticeable difference between lenses when the background is only a
little out of focus.

135/3.5

Zeiss Jena

MC-Sonnar

Overall effect: Pleasing

139/4.5

Bausch and Lomb

Tessar

Overall effect: Pleasing

120/2.8

Zeiss Jena

MC-Biometar

Not included due to faulty
aperture.

75-150/3.5

Nikon

Series E (at ~135)

Overall effect: Pleasing

120/2.8

Arsenal

Vega MC

Overall effect: Neutral,
background rendering too sharp (this would be enhanced
apparently depth of field, and would be desirable for most
applications, though)

70-200/4L

Canon (at ~135)

Overall effect: Pleasing

135/2.8

Canon (no SF)

Overall effect: Pleasing

85/2

Jupiter

Overall effect: Pleasing

Test Scenario 3, Background Doll More Distant,
f/4

This scenario gives a better notion of how smooth
the background rendering is with each lens.

135/3.5

Zeiss Jena

MC-Sonnar

Edge: Very slight bright-line

Double-line: None

Aperture shape: None

Overall effect: Pleasing, perhaps the best
in this test scenario.

139/4.5

Bausch and Lomb

Tessar

Edge: Pronounced bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: Yup, clumpy. Doesn't have
the smoothness of the Sonnar.

120/2.8

Zeiss Jena

MC-Biometar

Edge: Pronounced bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: Distracting

75-150/3.5

Nikon

Series E (at ~135)

Edge: Very slight bright-line

Double-line: None

Aperture shape: Slightly oval
(vignetting?)

Overall effect: Pleasing

120/2.8

Arsenal

Vega MC

Edge: Slight bright-line

Double-line: Apparent

Aperture shape: Slight

Overall effect: Not nearly as smooth as
most in the test.

70-200/4L

Canon (at ~135)

Edge: Slight bright-line

Double-line: Slight

Aperture shape: None (lens is wide open)

Overall effect: Pleasing, not quite as
smooth as the Sonnar

135/2.8

Canon (no SF)

Edge: Slight bright-line

Double-line: Slight

Aperture shape: Slight

Overall effect: Neutral, not quite as good
as the 70-200/4L

85/2

Jupiter (at f/2 to produce same apparent
focus)

Edge: Pronounced bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: Supposedly a Sonnar
design, but no match for the Sonnar in this test.

Test Scenario 3, Sonnar 180 and Canon 70-200, at
f/4

Think a zoom lens can't have good bokeh? Think
again.

180/2.8

Zeiss Jena

MC-Sonnar

Edge: The highlight fades at
the edge, but with a very slight bright edge on one side.

Double-line: None

Aperture shape: None

Overall effect: This is the classic Sonnar
look, with a very smooth rendering of the background.

70-200/4L

Canon (at ~200)

Edge: Faded edge

Double-line: None

Aperture shape: Slight oval.

Overall effect: Quite pleasing, and
outstanding for a zoom, even a high-end zoom. But the Sonnar has
the edge (or, rather, the lack of edge). In the face of the far
doll, there are some edges that are smoother in the Sonnar image

Test Scenario 3, All Lenses Faster Than f/4, Wide
Open.

Think a faster lens always provides better bokeh?
Think again. But if it's faster by a large margin, the difference in
focus may overcome a difference in bokeh. The best way to get the same
effect as a larger aperture, though, is to back up and use a longer
lens.

180/2.8

Zeiss Jena

MC-Sonnar

Edge: Faded

Double-line: None

Aperture shape: None

Overall effect: Wide, smooth brush. The
best of all the lenses (but comparisons are hard due to longer
focal length)

135/2.8

Canon (no SF)

Edge: Slight bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: No match for either
Sonnar. Even though this lens is faster than the 135/3.5 Sonnar,
the background rendering is not as smooth.

120/2.8

Arsenal

Vega MC

Edge: Moderate bright-line

Double-line: Apparent

Aperture shape: None

Overall effect: Distracting

120/2.8

Zeiss Jena

MC-Biometar

Edge: Pronounced bright-line

Double-line: Significant

Aperture shape: None

Overall effect: Distracting; worse than
the Vega. This is surprising--the Biometar is often the choice
for those who don't like the Vega's bokeh.

135/3.5

Zeiss Jena

MC-Sonnar

Edge: Very slight bright-line

Double-line: None

Aperture shape: None

Overall effect: Very smooth, and the best
of this test (except for the 180 Sonnar), despite being the
slowest lens in this test scenario.

What have we learned?

Bokeh has several components, including edge
effects around out-of-focus highlights and false edges in the
rendering of out-of-focus details.

Bokeh rendering is not the same in all
situations, and some lenses will be better than others in some
situations and worse in other situations. The Vega in this test has
produced some really ugly bokeh, not consistent with these results.
Lens bokeh is not a single value, and each lens requires
considerable experience to understand where it is good and where it
is not.

Sonnar designs don't necessarily have better
bokeh, but they have the potential.

Reputation for good bokeh (e.g., the Jupiter)
don't always show in actual results.

Lens complexity seems to have little bearing
on bokeh. Lens design, however, is paramount.

Apertures shapes are not really an issue with
bokeh, especially near wide open. In none of these tests was
aperture shape the main determinant in apparent bokeh quality. So,
we should stop counting aperture blades. The lens with the most
aperture blades was the B&L Tessar, but it had uniformly the worst
bokeh.